Ge掺杂碳化硅晶体的生长缺陷

采用物理气相传输法(PVT)制备了2英寸Ge掺杂和非掺SiC晶体, 并使用二次离子质谱仪(SIMS)、显微拉曼光谱(Raman spectra)仪、体式显微镜、激光共聚焦显微镜(LEXT)和高分辨X射线衍射(HRXRD)仪等测试手段对其进行了表征。结果表明, Ge元素可以有效地掺入SiC晶体材料中, 且掺杂浓度达到2.52×10¹⁸/cm³, 伴随生长过程中Ge组份的消耗和泄漏, 掺杂浓度逐渐降低; 生长初期高浓度Ge掺杂会促使6H-SiC向15R-SiC晶型转化, 并随着生长过程中Ge浓度的降低快速地转回6H-SiC稳定生长。用LEXT显微镜观察发现, 生长初期过高的Ge掺杂导致空洞明显增多, 位错密度增加, 掺杂晶体中位错密度较非掺晶体增大一倍。HRXRD分析表明掺Ge能增大SiC晶格常数, 这将有利于提高与外延III族氮化物材料适配度, 并改善器件的性能。     

CdZnTe晶体表面Au电极薄膜的制备及其欧姆接触性质

为了研究不同制备工艺对电极欧姆接触特性的影响, 分别采用真空蒸发法、溅射法及化学沉积法在CdZnTe晶片表面制备了Au薄膜电极, 通过测试样品的SEM、I-V曲线及交流阻抗谱, 研究了不同电极制备工艺及退火处理对Au薄膜电极的微观结构及欧姆接触特性的影响。结果表明化学沉积法制备的Au薄膜表面更加平整、致密, 接触势垒的高度较低, 电极欧姆接触特性最好。退火处理可以改善电极的欧姆接触特性, 100℃退火后, 化学沉积法制备的Au电极的欧姆系数由0.883提高至0.915, 势垒高度由0.492降低至0.487 eV。交流阻抗谱分析表明, 化学沉积法制备电极具有最低的接触势垒, 这与界面处晶片表面的掺杂及缺陷的变化有关。     

Au/p-CdZnTe欧姆接触的电学测量及界面特性分析

采用化学镀金法在高阻p-CZT(CdZnTe)晶片表面制备Au电极,并用改进的圆环传输线模型(Ring-CTLM)测量了CZT电极的接触电阻,探讨了大气气氛下退火温度对CZT电极欧姆特性的影响.实验结果表明,200℃退火可以显著改善欧姆特性,使接触电阻率ρc显著减小,采用Ring-CTLM模型测得CZT与金电极接触电阻率为0.1524Ω·cm2.通过XPS分析了CZT与Au电极接触界面的成分,发现在Au/p-CdZnTe界面处形成了CdTeO3层,该界面层可起到载流子复合中心的作用,构建的新模型很好地解释了化学镀金法在p-CdZnTe晶片表面形成欧姆接触的机理.     

Fe3+离子敏感Ge-Sb-Se-Fe(Ni)系薄膜的掺杂行为研究

本文用电子束蒸发方法制备了掺Fe、Ni的Ge-Sb-Se-Fe(Ni)薄膜.Hall效应测得薄膜均为p型半导体.对薄膜的研究表明Ge-Sb-Se中不同过渡金属元素掺杂因失电子能力差异而形成了不同的网络结构,高电负性过渡金属元素掺杂倾向于形成较少缺陷态的网络结构;Al的热扩散共掺杂使载流子浓度提高,且其浓度的提高可以抵消杂质散射引起的迁移率下降,降低薄膜的方块电阻.     

PI柔性衬底上Ga掺杂ZnO透明导电薄膜的常温制备及特性研究

采用射频(RF)磁控溅射技术在室温条件下制备了基于柔性PI衬底上不同氧化镓(Ga_2O_3)掺杂浓度的ZnO(GZO)薄膜。研究发现,在Ga_2O_3掺杂浓度为5%(质量比)情况下,制备的GZO薄膜具有最优化的光电特性,其对应电阻率为5.85×10~(-4)Ω·cm,Hall迁移率为14.6 cm~2·V~(-1)·s~(-1),载流子浓度为7.33×1020cm~(-3),可见光区平均透过率为86.5%。经过1000次弯折测试后,垂直于折痕方向的电阻明显增大,而平行于折痕方向的电阻变化相对较小。基于以上结果,可以得出所制备的GZO薄膜具备优异的光电特性,有望应用于各种柔性光电设备。     

2.5GDFB量子阱激光器p型欧姆接触电极的研究

对2.5GDFB量子阱激光器p型低阻欧姆接触电极进行了研究,在退火温度400℃,退火时间30s进行快速热退火条件下,对Au-Pt-Ti/InAs/p+-InGaAs(掺Zn>1×1019cm-3)/MQW/n-InP和Au-Pt-Ti/p+-InGaAs(掺Zn>1×1019cm-3)/MQW/n-InP两种结构进行了p型欧姆接触试验研究,并对两者串联电阻进行了比较,其结果前者的串联电阻阻值为后者的1/4.     

共掺浓度对Na-Al共掺杂ZnO薄膜微观结构和光电性能的影响

在石英玻璃衬底上,通过溶胶-凝胶旋涂法制备得到钠铝(Na-Al)共掺氧化锌(ZnO)薄膜(NAZO)。研究不同NaAl共掺杂浓度对ZnO薄膜的结晶性、微观结构、光电性能的影响。结果表明:所有NAZO薄膜样品都沿c轴择优取向生长;适当的Na-Al共掺浓度,可以提高ZnO薄膜结晶性,提高薄膜的载流子迁移率;同时还可以观察到NAZO薄膜表面生长出六角柱状结构晶粒。随着Na-Al元素掺杂浓度的改变,所获薄膜的最高平均光学透过率达到95%。由于元素间固溶比的不同,适当的浓度可以提高Na-Al元素的掺杂效率和薄膜内部的载流子浓度,降低薄膜电阻率,NAZO薄膜最低电阻率为4.7×10-2Ω·cm。     

氢气氛退火对硅上低温外延制备的硅锗薄膜性能的影响

采用反应型热化学气相沉积系统在硅(100)衬底上外延生长富锗硅锗薄膜。四氟化锗作为锗源, 乙硅烷作为还原性气体。通过设计表面反应, 在低温条件下(350℃)制备了高质量的富锗硅锗薄膜。研究了氢退火对低温硅锗外延薄膜微结构和电学性能的影响。结果发现退火温度高于700℃时, 外延薄膜的表面形貌随着退火温度的升高迅速恶化。当退火温度为650℃时, 获得了最佳的退火效果。在该退火条件下, 外延薄膜的螺旋位错密度从3.7×10⁶ cm^-2下降到4.3×10⁵ cm^-2, 表面粗糙度从1.27 nm下降到1.18 nm, 而外延薄膜的结晶质量也有效提高。霍尔效应测试表明, 经退火处理的样品载流子迁移率明显提高。这些结果表明, 经过氢退火处理后, 反应型热化学气相沉积制备的低温硅锗外延薄膜可以获得与高温下硅锗外延薄膜相比拟的性能。     

Au电极与CdMnTe晶体的表面接触电阻率研究

采用圆形传输线模型研究了金(Au)电极与碲锰镉(CdMnTe)晶体的欧姆接触特性,Au电极采用AuCl3化学镀金法制备,计算了其接触电阻率。实验探讨了表面处理和退火对Au/CdMnTe接触电阻率的影响。结果表明,CdMnTe晶体经过化学抛光和化学机械抛光后Au/CdMnTe的接触电阻率分别为544.5和89.0Ω·cm2。通过AFM与XPS分析了晶体表面的形貌与成分,发现表面粗糙度和富Te成分对CdMnTe薄层电阻和载流子传输长度有较大的影响,决定了接触电阻率的大小。在150℃空气气氛退火1h后,经CP和CMP表面处理的样品,Au/CdMnTe接触电阻率均减小,分别为313.6和30.2Ω·cm2。退火促进了Au向CdMnTe晶体的扩散,使接触电阻率进一步降低,欧姆接触性能提高。     

4H-SiC晶体中的层错研究

采用物理气相传输法(PVT法)在4英寸(1英寸=25.4 mm)偏<11¯20>方向4°的4H-SiC籽晶的C面生长4H-SiC晶体。用熔融氢氧化钾腐蚀4H-SiC晶体, 并利用光学显微镜研究了晶体中的堆垛层错缺陷的形貌特征和生长过程中氮掺杂对4H-SiC晶体中堆垛层错缺陷的影响。结果显示, 4H-SiC晶片表面的基平面位错缺陷的连线对应于晶体中的堆垛层错, 并且该连线的方向平行于<1¯100>方向。相对于非故意氮掺杂生长的4H-SiC晶体, 氮掺杂生长的4H-SiC晶体中堆垛层错显著偏多。然而, 在氮掺杂生长的4H-SiC晶体的小面区域, 虽然氮浓度高于其他非小面区域, 但是该小面区域并没有堆垛层错缺陷存在, 推测这主要是由于4H-SiC晶体小面区域特有的晶体生长习性导致的。     

Codoping of Ge with Al and Sb

Ge single crystals were doped with Al or Sb to various concentrations and codoped with Al and Sb in the ratios 3:1, 1:1, and 1 : 3. Using Hall effect measurements, the electron and hole concentrations in the doped crystals were determined. A relationship between the dopant-solubility limits and the maximum carrier concentration was found. The data obtained were shown to be consistent with the processes Al ↔ Al^- + h and Sb ↔ Sb⁺ + e in Ge doped with Al or Sb up to the solubility limit. In the material codoped with Al and Sb in the atomic ratio 3 : 1, the hole concentration is equal to the difference in the Al and Sb concentrations. At an Al : Sb ratio of 1 : 3, the electron concentration in Ge(Al, Sb) is higher than that in Ge<Sb> because of the increase in Sb solubility in the presence of Al. The crystals doped with equal concentrations of Al and Sb aren-type. The results are interpreted in terms of donor-acceptor interaction and compensation effect.     

Improved Al/Si ohmic contacts to p-type 4H-SiC

An AlSi-based ohmic contact with a new composition is reported in this paper. AlSi(2%)Ti(0.15%) contacts are formed by evaporation on p-type 4H-SiC grown by liquid phase epitaxy (LPE) and annealed in the temperature range from 700 to 950°C. The ohmic behaviour has been checked by I–V characteristics and the contact resistivity has been measured by the linear transmission-line-model (TLM) method. The dependence of the contact resistivity on the annealing conditions has been studied. An ohmic behaviour has been established at 700°C while the lowest contact resistivity value of 9.6×10⁻⁵ Ω cm² has been obtained after annealing at 950°C. The thermal stability of both Al/Si/SiC and AlSiTi/SiC contacts at a temperature of 600°C has been studied. It has been found that the AlSiTi/SiC contacts are stable for 100 h at this ageing temperature while the Al/Si/SiC contacts deteriorate after 24 h.     

P-type InP grown by liquid phase epitaxy with rare earths: not intentional Ge acceptor doping

InP single crystal layers were grown by liquid phase epitaxy (LPE) on semi-insulating InP:Fe substrates with praseodymium added to the melt. Room temperature Hall effect measurements revealed p-type conductivity of the layers with the hole concentration 6×10¹⁴ cm⁻³ and mobility 150 cm² V⁻¹ s⁻¹. By measuring temperature dependence of the hole concentration the binding energy of the dominant acceptor was determined as 223 meV. A photoluminescence line was found at 1.195 eV, close to the previously estimated no-phonon line of Ge acceptor transitions in Ge doped n-type InP. It was concluded that Ge acceptors cause the p-type conductivity of the grown layers.     

Cr~（3＋）离子掺杂对Al_2O_3粉末结构及发光性能影响

采用球磨法制备了不同浓度Cr_2O_3掺杂的Al_2O_3粉体,并在700℃、1200℃空气中退火2 h。1200℃退火后样品,除掺杂浓度为1.6%的样品中出现少量γ-Al_2O_3相外,其余样品相均为纯α-Al_2O_3。样品晶格常数随着Cr~（3＋）离子浓度的增加而增加。采用波长为579 nm的激发光源对佯品进行荧...     

Investigation of the effect of rare earth doping on the electrical and photovoltaic properties of chromotrope 2R thin film devices

Praseodymium (Pr) doped and Samarium (Sm) doped chromotrope 2R (CHR) were used for the fabrication of Schottky devices, by the spin coating technique. The diode in which doped CHR behaves as an n-type organic semiconductor exhibits rectification behaviour in the dark. Doping with rare earths imparts an accelerated improvement in the n-type conductivity as well as in the rectification effect. The observed rectification effects are explained by n-type semiconductivity of the doped CHR thin films. The formation of a blocking contact (Schottky barrier) indium tin oxide with (ITO) electrode and an ohmic contact with Al or ln, also confirms its n-type behaviour. The position of the Fermi level shifts toward the conduction band edge on rare earth doping. Additionally, the concentration of free carriers and mobility of electrons also increase upon doping, with the simultaneous decrease in trap concentration. Various electrical parameters such as barrier height (b), density of ionized donor (Ns) and depletion layer width (W) were calculated from the detail capacitance–voltage analysis of (C–V) characteristics. The photo-action spectra of the devices and absorption spectra of doped CHR layer reveal the formation of a Schottky barrier at the ITO-doped CHR interface and an Ohmic contact at the Al-doped CHR interface. Photovoltaic measurements of these devices provide parameters such as short circuit photocurrent (Jsc), open circuit voltage (Voc), fill factor (FF) and power conversion efficiency (). The effect of rare earth doping on the electrical and photovoltaic parameters are discussed in detail. © 1998 Chapman & Hall     

Ge/Pd/n-GaAs低阻欧姆接触的SIMS分析

采用Ge／Pd／GaAs结构和快速热退火在n－GaAs上形成了低阻欧姆接触。利用H次离子质谱（SIMS）技术揭示和讨论了低欧姆接触形成的机理。比较了采用X 和CsX 信号检测的Ge，Pd，Ga和As的深度分布。结果表明采用CSX 可以提供更准确的结果和成分信息。     

三嗪对CVD石墨烯n型掺杂的研究

以化学气相沉积(CVD)制备的单层石墨烯为原料, 小分子三嗪为掺杂剂, 采用吸附掺杂的方式, 在低温下对石墨烯实现n型掺杂。利用拉曼光谱(Raman)、X射线光电子能谱分析(XPS)、原子力显微镜(AFM)、紫外分光光度计(UV)和霍尔效应测试仪(Hall)对样品的形貌、结构及电学性能进行表征。结果表明: 该方法简单安全, 能够对石墨烯实现均匀的n型掺杂, 掺杂石墨烯的透光率达到95%。掺杂后石墨烯的特征峰G峰和2D峰向高波数移动。掺杂180 min后, 载流子浓度达到4×10¹²/cm², 接近掺杂前的载流子浓度, 掺杂后的石墨烯在450℃的退火温度下具有可逆能力, 其表面电阻在300℃以下具有较好的稳定性。     

固相法制备钇掺杂的钛酸钡锶钙陶瓷的介电和热释电性能

采用固相反应法制备了Y掺杂 (Ba_0.6Sr_0.3Ca_0.1)_1-xY_xTi_0.999Mn_0.001O₃ (0≤x≤0.007)陶瓷, 重点研究了Y含量对BSCT基陶瓷的显微结构、介电性能和热释电性能的影响。结果表明: 随着Y含量的增加, BSCY_xTM陶瓷的平均晶粒尺寸逐渐减小, 介电常数、介电损耗、居里温度和热释电系数均呈现先增加后减小的趋势。当Y掺杂量为0.7mol%时, BSCY_xTM陶瓷的平均晶粒尺寸最小为3.1 μm, 且探测优值F_d较大, 最大值可达8.22×10^-5 Pa^-1/2(700 V/mm, 30℃), 高于采用溶胶-凝胶法制备的同组分陶瓷的探测优值5.91×10^-5 Pa^-1/2。     

Selective and non-selective growth by GSMBE/ULPCVD for heterojunction bipolar transistors

The challenges for thin film epitaxial techniques for the realisation of HBT device structures are: providing a high contrast between selective epitaxial growth (SEG) and non-selective epitaxial growth (NSEG) on patterned substrates; and fine control of the Ge concentration profile in the base region and the doping levels for all layers. A Gas Source MBE system has been modified for operation either in the conventional GSMBE mode or an Ultra Low Pressure CVD mode, namely the ‘by-pass mode’. This allows use of two growth modes to achieve the specified device structures. In particular, it has been demonstrated that a high As doping level (1.1×10¹⁸ cm⁻³) at a relatively low growth temperature and a rapid conversion to the non-selective mode, can be obtained using the by-pass mode. Non-graded and graded HBT test structures have been grown and characterised by SIMS and X-ray diffraction in order to calibrate the doping levels, the Ge concentration in the base region and the thickness of the layers.